Unburned fuel and other combustion products may escape past the piston and valve guides of an internal combustion engine (e.g., an internal combustion engine of a vehicle) into the crankcase. The resulting gases in the crankcase, often referred to as “blow-by” gases, may contribute to the formation of sludge in the engine oil supply. Further, blow-by gases may excessively pressurize the crankcase, resulting in undesirable leakage of oil pan gasket and crankcase seals. To avoid these issues, an engine may include a crankcase ventilation (CV) system coupled to the intake, which serves to vent blow-by gases from the crankcase to the intake. The CV system may include a passive crankcase ventilation (CV) valve intermediate the crankcase and the engine intake passage, to regulate the flow of blow-by gases from the crankcase to the intake manifold.
An example crankcase ventilation system is shown by Pursifull et al. in U.S. Pat. No. 8,925,520. Herein, crankcase gases are directed through an aspirator to generate vacuum that is supplied to a vacuum consumer. The example system in U.S. Pat. No. 8,925,520 includes a passive control valve for regulating crankcase ventilation into the aspirator and into an intake manifold. The passive control valve is arranged intermediate a crankcase and the intake manifold.
Various types of CV valves may be used in CV systems to regulate crankcase ventilation flow. In one example, the CV valve may enable a higher flow rate of crankcase gases into the intake manifold in the case of low (or shallow) intake manifold vacuum. During conditions when the intake manifold has a lower vacuum (e.g., shallow vacuum such as 0-15 kPa), the engine has a larger air flow rate and can accept a larger crankcase ventilation flow rate. In the case of higher levels of intake manifold vacuum (e.g. deeper such as vacuum deeper than 80 kPa), such as during engine idle conditions, the CV valve may be substantially closed, and a smaller ventilation flow rate of crankcase gases may be allowed therethrough. Thus, the CV valve controls (e.g., limits) the flow of crankcase vapors into the intake manifold during idle conditions in order to reduce the idle air flow rate and thereby, limit engine air consumption at idle.
The inventors herein have recognized potential issues with the example system of U.S. Pat. No. 8,925,520. As an example, vacuum generation by the aspirator using crankcase ventilation flow may be insufficient during certain engine conditions. For example, when intake manifold vacuum is in the range of 20-80 kPa, the flow rate of crankcase vapors allowed into the intake manifold via the CV valve may be lower. This lower flow rate of crankcase vapors may not generate sufficient vacuum for the vacuum consumer. Further still, even though the vacuum consumer may be fluidically coupled to the intake manifold, vacuum levels in the intake manifold may be inadequate for direct replenishment of the vacuum consumer.
The inventors herein have identified an approach to at least partly address the above issue. In one example approach, a method for an engine comprises selectively enabling one of crankcase ventilation flow and aspirator motive flow via an electrically controlled valve responsive to a desired engine air flow and a demand for vacuum from a vacuum consumer. In this way, demand for vacuum by the vacuum consumer may be met during various engine conditions.
As one example, an engine may include an electrically controlled valve that may fluidically couple each of a crankcase and an aspirator to an intake manifold of the engine. The aspirator may, in turn, be coupled to a vacuum consumer. The electrically controlled valve may be configured to allow crankcase ventilation flow into the intake manifold for a larger duration of engine operation. However, when the vacuum consumer demands vacuum, the electrically controlled valve may be adjusted to enable motive flow through the aspirator while obstructing crankcase ventilation. Motive flow through the aspirator may generate vacuum that can be provided to the vacuum consumer.
In this way, each of crankcase ventilation and vacuum generation via an aspirator may be actively controlled. Vacuum may be generated for a vacuum consumer even when there is insufficient crankcase ventilation flow. Further, the crankcase may be purged of vapors when vacuum generation is not desired. Thus, crankcase ventilation may be increased while providing vacuum generation when desired. By using a single valve to control each of crankcase ventilation and vacuum generation at the aspirator, component expenses may be reduced. Further still, additional control valves, such as an aspirator shut-off valve that controls motive flow through the aspirator, may not be needed. Accordingly, costs may be reduced while also reducing packaging issues. As such, since brake vacuum replenishment may be desired occasionally and crankcase ventilation may not need to occur continuously, crankcase ventilation may be interrupted temporarily for enabling recovery of brake vacuum when desired.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.